The Kirchhoff’s law on emission and absorption of thermal radiation is a law driven deductively for the energy equilibrium of thermal radiation. First, we consider on the basis of spectroscopic experiments and an electromagnetism whether the Kirchhoff’s law is valid for the spectra of emission and absorption of an electromagnetic wave which are characterized by the phase as well as the amplitude of the wave. The interference of radiation caused by the phase matching is a key for this problem. Second, we consider the possibility of systematic coherency of spherical waves emitted by a number of dipoles which are the sources of thermal radiation. This consideration is related to the validity of the assumption that emission sources of thermal radiation move randomly.

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